JPS6113418B2 - - Google Patents

Description

[Detailed Description of the Invention] In a public address system that installs one or more speakers in a certain venue, listens to attendees with microphones, and amplifies the sound from the speakers, the microphones are placed near the speakers. When it comes, it makes a howling sound. For this reason, a transmitter that emits a certain signal is placed near the microphone, and a receiver is placed near the speaker, so that when the microphone approaches the speaker, the signal from the transmitter is received by the receiver. A method has been proposed to prevent howling by attenuating the signal supplied from the microphone to the speaker.

In this case, specifically, the transmitter and receiver are
It should have a configuration that utilizes electromagnetic induction. That is, the transmitter causes a high frequency current of, for example, 1 MHz to flow through the transmitting coil to radiate induced magnetic flux, while the receiver detects the induced magnetic flux radiated from the transmitter using the receiving coil.

By the way, in this case, the magnitude of the voltage induced in the receiving coil changes depending on the angle that the induced magnetic flux from the transmitting coil makes with respect to the receiving coil, and especially when the magnetic flux is orthogonal to the receiving coil, the voltage changes. This causes the inconvenience that howling is not prevented even when the microphone is brought close to the speaker, and the operation becomes unstable.

The present invention is designed to avoid such inconveniences by devising the configuration of the inductive receiver.

In this invention, as shown in FIG. 1, two receiving coils are provided orthogonal to each other. In other words, the core 11A is wound with the coil 12A, and the core 1
A coil 12B wound around a coil 1B is arranged orthogonally to the coil 12B.

Then, the induced magnetic flux H from the transmitting coil is made to follow the plane where the receiving coils 12A and 12B exist, as shown in the figure. For example, as shown in FIG.
2A and 12B are arranged orthogonally in a plane parallel to the plane of the paper so that the induced magnetic flux H from the transmitting coil 5 disposed near the microphone 4 also exists in the plane parallel to the plane of the paper.

Furthermore, in this invention, as shown in FIG.
The signal obtained by one receiving coil 12B is supplied to a phase shifter 13 to shift the phase by 90 degrees, and this phase-shifted signal and the signal obtained to the other receiving coil 12A are supplied to an adder 14 and added. , the sum signal is supplied to a detector 16 through an amplifier 15 for detection, and a detected output is obtained at an output terminal 17.

As mentioned above, when a high frequency current of 1 MHz, for example, is passed through the transmitting coil, the wavelength of the electromagnetic wave from this point is
The distance is 300m, which is much longer than the distance between the transmitter and receiver. Then, when the wavelength of the signal from the transmitting coil is sufficiently long compared to the distance between the transmitter and the receiver, the receiving coils 12A and 12B
The voltages induced in the two are always in phase or out of phase.

Therefore, if the distance between the transmitter and the receiver is r, the angle between the magnetic flux H and the receiving coil 12A is θ, and the angular frequency of the magnetic flux H is ω, then the receiving coils 12A and 12
The voltages e ₁ and e ₂ induced in B are as follows: e ₁ =G/r ³ cosθcosωt (1) e ₂ =G/r ³ sinθcosωt or −G/r ³ sinθcosωt (2). However, G is a constant. Therefore,
The output voltage e′ ₂ of the phase shifter 13 is e′ ₂ =G/r ³ sinθsinωt or −G/r ³ sinθsinωt (3), and the output voltage e of the adder 14 is e=e ₁ +e′ ₂ = G/r ³ (cos θ cos ωt + sin θ sin ωt) or G/r ₃ (cos θ cos ωt - sin θ sin ωt) = G/r ³ cos (ωt - θ) or G/r ³ cos (ωt
+θ) ...(4).

That is, even if the angle θ between the magnetic flux H and the receiving coil 12A changes, the added voltage e changes only in phase and does not change in amplitude. Therefore, the output terminal 17 has a detected voltage whose magnitude does not change depending on the angle θ formed between the magnetic flux H and the receiving coil 12A.
A DC voltage whose magnitude varies depending on the distance r between the transmitter and the receiver is obtained.

Therefore, the distance between the transmitter and receiver can be reliably detected using this detection voltage, and howling can be reliably prevented when the transmitter approaches the receiver, that is, within the range of the microphone and the speaker. Become so.

Note that, when the signal is in a narrow band, the phase shifter 13 shifts the buffer 2 as shown in FIG. 4, for example.
1, inverter 22, resistor 23, capacitor 24
and a buffer 25, and a resistor 2
If the value of 3 is R and the capacitance of the capacitor 24 is C, then 1/RC=ω may be satisfied.

As described above, according to the present invention, stable operation can be expected and howling can be reliably prevented.

Note that in the case of a public address system having a plurality of speakers, a receiver having the above-described configuration may be placed near each speaker.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the arrangement of the receiving coils of a receiver according to the present invention, FIG. 2 is a diagram showing the configuration of a loudspeaker, and FIG. 3 is a system diagram of the receiver according to the present invention.
FIG. 4 is a connection diagram of a specific example. 12A and 12B are receiving coils, and 13 is a phase shifter.

Claims (1)

[Claims] 1 It has two receiving coils arranged perpendicular to each other, and the signal obtained from one of the receiving coils is 90
An inductive receiver for howling prevention in which the phase is shifted, the phase-shifted signal and the signal obtained at the other receiving coil are added, and the added signal is detected.